This invention relates in general to the field of telecommunications, more precisely to Wireless Local Area Networks (WLAN) and Electrical and Electronics Engineers (IEEE) 802.11 WLAN standard.
The IEEE 802.11 Wireless Local Area Network specification specifies a so-called Contention Free Period (CFP), which is a period of transmission time that is free from the normal contention based airtime reservation. The length and duration of CFP are configurable parameters in Access Point (AP), so that the start of CFP is repeated after one or more Delivery Traffic Indication Message (DTIM) intervals (see IEEE 802.11 standard). The CFP and its relationship to the so-called Content Period (CP) is schematically illustrated in FIG. 12. As can be seen, a CFP repetition interval contains a Content Free Period (CFP) and a Content Period (CP). Each CFP begins with a beacon frame that contains a DTIM element.
The purpose of this CFP is that it can be used for delivering high priority traffic, which has higher real time requirements than normal traffic. The CFP is controlled by the so-called Point Coordination Function (PCF) in an Access Point (AP). The standard specifies the PCF operation in basic level, but does not specify how the PCF should be controlled or how some traffic should be identified as high priority traffic. These things are considered to be out of the scope of the standard.
Information within data frames is marked as having a high priority by using certain fields in some protocol frames or headers. However, the Access Point (AP) usually processes only frames on the Medium Access Control (MAC) layer such that the AP can not easily access information regarding the priority of certain data blocks within the frames, since this information is processed in higher layers.
Thus, for getting priority information, conventionally the frames which are to be transmitted through an Access Point (AP) had to be searched for these fields which indicate the priority state of the actual data frame. This means that in all frames all fields had to be checked, all the headers had to be analyzed, starting from the outer most headers, until the right field in the header had been found.
Since all frame headers are parsed when detecting priority, this measure has a high reliability.
However, this measure is very complex, takes a long time and requires a large amount of processing. Furthermore, the traffic transferred in WLAN can be practically anything, including complex tunneling protocols. Therefore, all the frame headers and protocols which can be included in the data frames transmitted via the network have to be known. Hence, the amount of information needed for identifying the data is huge. This huge amount of information is typically too heavy to handle in quite small and low price equipment like WLAN access points (AP).
In addition, it has to be considered that every time new protocols are introduced, the access point has to be updated, at least by software updates. This is also required in case protocols already used are changed.
Thus, conventionally such a transmission differentiation based on priority was not conducted at all. That is, the existing systems according to the IEEE 802.11 standard do not separate traffic based on priority. In these conventional systems, the Content Free Period (CFP) is only used to deliver traffic from the Access Point (AP) to stations, treating all frames equally.